Alumina is a well known catalyst support and a catalyst. It is also well known that the properties of alumina can be modified in various ways such as by cogelling with silica to form a silica/alumina composite or by incorporating phosphorus to give an alumina/phosphate composite. These modified aluminas are useful in catalyzing various hydrocarbon conversion processes such as hydrocracking, isomerization and alkylation. The prior art shows several ways of preparing these materials which are summarized below.
U.S. Pat. No. 3,909,450 discloses a method of preparing an amorphous silica/alumina composition in which sols of alumina and silica are mixed and then gelled by the well known oil drop method and finally dried to provide the composition. A silica/alumina composition can also be prepared by coprecipitation as described in U.S. Pat. No. 3,274,124.
U.S. Pat. Nos. 4,629,717 and 4,727,209 describe a phosphorus modified alumina composite and hydrocarbon conversion processes using the composite. The composite is amorphous and has a phosphorus to aluminum molar ratio of about 1:1 to 1:100 and has a surface area of about 140 to 450 m.sup.2 /g.
U.S. Pat. No. 4,760,040 discloses a hydrocarbon cracking catalyst which is composed of a crystalline aluminosilicate zeolite in a phosphorus containing alumina matrix. Similarly U.S. Pat. No. 4,243,556 describes a composition containing silica and alumina, the alumina being promoted by at least one element or compound selected from sodium, manganese and phosphorus. Additionally, U.S. Pat. No. 4,158,621 describes a catalyst comprising an alumina-aluminumphosphate-silica matrix which is amorphous after calcination at 500.degree. C. for 16 hours.
Crystalline silicoaluminophosphates are disclosed in U.S. Pat. No. 4,440,871 while crystalline aluminum phosphates are disclosed in U.S. Pat. No. 4,310,440. Japanese Public Disclosure J01207389-A discloses a catalyst for purifying a hydrocarbon which consists of a support including silica/alumina, the support having dispersed on it phosphoric acid. Finally, Japanese Public Disclosure J60018509-A describes a catalyst which is a mixture of P.sub.2 O.sub.5 and silica/alumina.
In contrast to this prior art, applicants have prepared a catalytic composite whihc comprises an amorphous solid solution of phosphorus, aluminum and silicon oxides (hereinafter referred to as an amorphous silica/alumina/phosphate). Generally a solid solution is simply a solid phase containing more than one component. One class of solid solution is a substitutional solid solution in which solute atoms or groups of atoms are substituted for solvent atoms or groups in the crystal structure. The substitution of one atom or groups for another is possible only when the substituents do not differ greatly in size. Thus, in the present system phosphorus and silicon atoms have been substituted into positions ordinarily occupied by aluminum atoms. Clearly this is different from the systems in which phosphoric acid or other phosphorus compounds are impregnated onto an alumina or a silica/alumina substrate or support. It is also different from Japanese Public Disclosure J60018509-A in that there is no separate P.sub.2 O.sub.5 phase which has been mixed in with a silica/alumina powder.
The properties of the instant catalytic composite are also different from the heterogeneous materials described in the prior art. For example, the acidity of the instant catalyst is derived from the amount of silica present in the composition whereas in prior art catalysts it is primarily derived from the presence of free phosphate on the catalyst. Also the porosity of the instant catalyst is controlled by polymer packing during gelation of the catalyst particles.